Silicon based lithium ion battery and improved cycle life of same

ABSTRACT

Silicon-dominate battery electrodes, battery cells utilizing the silicon-dominate battery electrodes, and methods of manufacturing are disclosed. Such a battery cell includes a cathode, a separator, an electrolyte, and an anode. The anode comprises a current collector and active material on the current collector. The active material layer includes at least 50% silicon. A ratio of the electrolyte to Ah is over 2 g/Ah.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/532,739, filed Nov. 22, 2021, which is a divisional of U.S.application Ser. No. 17/532,549, filed Nov. 22, 2021, the entireties ofwhich are hereby incorporated by reference.

FIELD

Aspects of the present disclosure relate to energy generation andstorage. More specifically, certain embodiments of the disclosure aredirected to battery electrodes, battery cells, and/or batteries withimproved cycle life.

BACKGROUND

A rechargeable battery experiences periods of charging and periodsdischarging. These charge-discharge cycles reduce a storage capacity ofthe of battery and thus reduce the life of the battery.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present disclosureas set forth in the remainder of the present application with referenceto the drawings.

BRIEF SUMMARY

A battery and/or battery anode are substantially shown in and/ordescribed in connection with at least one of the figures, as set forthmore completely in the claims.

These and other advantages, aspects and novel features of the presentdisclosure, as well as details of an illustrated embodiment thereof,will be more fully understood from the following description anddrawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a battery with a silicon-dominant anode, inaccordance with an example embodiment of the disclosure.

FIG. 2A is a flow diagram of a direct coating process for fabricating acell with a silicon-dominant electrode, in accordance with an exampleembodiment of the disclosure.

FIG. 2B is a flow diagram for of an alternative process for laminationof electrodes, in accordance with an example embodiment of thedisclosure.

FIG. 3 illustrates slurry viscosity versus mixing time, in accordancewith an example embodiment of the disclosure.

FIG. 4 illustrates the results of thermal gravimetric analysis (TGA) ofdry WPAI, in accordance with an example embodiment of the disclosure.

FIG. 5 illustrates an adhesion test for a silicon-dominant anode withwater-soluble acidified PAI and water-based acidic polymer solutionadditive, in accordance with an example embodiment of the disclosure.

FIG. 6 illustrates a silicon-dominant anode after a winding test, inaccordance with an example embodiment of the disclosure.

FIG. 7 illustrates normalized discharge capacity of a cell withwater-soluble acidified PAI and water-based acidic polymer solutionadditive anode compared to a standard cell with NMP-based slurrylaminated anode, in accordance with an example embodiment of thedisclosure.

FIG. 8 illustrates slurry viscosity versus temperature, in accordancewith an example embodiment of the disclosure.

FIG. 9 illustrates electrochemical performance of anodes in pouch cells,in accordance with an example embodiment of the disclosure.

FIG. 10 illustrates capacity retention of single-layer and five-layerpouch cells during cycle life based on 2C(4.2V)/0.5C(2.75V) cycles.

FIG. 11 illustrates capacity retention of single-layer and five-layerpouch cells during cycle life based on 4C (4.2 V)/0.5C (3.2 V) cycles.

FIG. 12 illustrates capacity retention of pressed and not pressed pouchcells during cycle life based on 2C (4.2 V)/0.5C (2.75 V) cycles.

FIG. 13 illustrates capacity retention of single-layer pouch cellshaving anodes manufacture per three different formulations.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a battery with silicon-dominant anodes, inaccordance with an example embodiment of the disclosure. Referring toFIG. 1 , there is shown a battery 100 comprising a separator 103sandwiched between an anode 101 and a cathode 105, with currentcollectors 107A and 107B. There is also shown a load 109 coupled to thebattery 100 illustrating instances when the battery 100 is in dischargemode. In this disclosure, the term “battery” may be used to indicate asingle electrochemical cell, a plurality of electrochemical cells formedinto a module, and/or a plurality of modules formed into a pack.Furthermore, the cell shown in FIG. 1 is a very simplified examplemerely to show the principle of operation of a lithium ion cell.Examples of realistic structures are shown to the right in FIG. 1 ,where stacks of electrodes and separators are utilized, with electrodecoatings typically on both sides of the current collectors. The stacksmay be formed into different shapes, such as a coin cell, cylindricalcell, or prismatic cell, for example.

The development of portable electronic devices and electrification oftransportation drive the need for high performance electrochemicalenergy storage. Small-scale (<100 Wh) to large-scale (>10 KWh) devicesprimarily use lithium-ion (Li-ion) batteries over other rechargeablebattery chemistries due to their high-performance.

The anode 101 and cathode 105, along with the current collectors 107Aand 107B, may comprise the electrodes, which may comprise plates orfilms within, or containing, an electrolyte material, where the platesmay provide a physical barrier for containing the electrolyte as well asa conductive contact to external structures. In other embodiments, theanode/cathode plates are immersed in electrolyte while an outer casingprovides electrolyte containment. The anode 101 and cathode areelectrically coupled to the current collectors 107A and 1078, whichcomprise metal or other conductive material for providing electricalcontact to the electrodes as well as physical support for the electrodecoating layer in forming electrodes.

The configuration shown in FIG. 1 illustrates the battery 100 indischarge mode, whereas in a charging configuration, the load 109 may bereplaced with a charger to reverse the process. In one class ofbatteries, the separator 103 is generally a film material, made of anelectrically insulating polymer, for example, that prevents electronsfrom flowing from anode 101 to cathode 105, or vice versa, while beingporous enough to allow ions to pass through the separator 103.Typically, the separator 103, cathode 105, and anode 101 materials areindividually formed into sheets, films, or coated foils. Sheets of thecathode, separator and anode are subsequently stacked or rolled with theseparator 103 separating the cathode 105 and anode 101 to form thebattery 100. In some embodiments, the separator 103 is a sheet andgenerally utilizes winding methods and stacking in its manufacture. Inthese methods, the anodes, cathodes, and current collectors (e.g.,electrodes) may comprise films.

In some embodiments, one or more of the electrodes is a silicon-dominantelectrode. In some embodiments, the electrode comprises aself-supporting composite material film. In some embodiments, thecomposite material film comprises greater than 0% and less than about90% by weight of silicon particles, and greater than 0% and less thanabout 90% by weight of one or more types of carbon phases, wherein atleast one of the one or more types of carbon phases is a substantiallycontinuous phase that holds the composite material film together suchthat the silicon particles are distributed throughout the compositematerial film.

The amount of silicon in the composite material can be greater than zeropercent by weight of the mixture and composite material. In certainembodiments, the mixture comprises an amount of silicon, the amountbeing within a range of from about 0% to about 90% by weight, such asgreater than 70%, or including from about 30% to about 80% by weight ofthe mixture. The amount of silicon in the composite material can bewithin a range of from about 0% to about 35% by weight, including fromabout 0% to about 25% by weight, from about 10% to about 35% by weight,and about 20% by weight. In further certain embodiments, the amount ofsilicon in the mixture is at least about 30% by weight. Additionalembodiments of the amount of silicon in the composite material includemore than about 50% by weight, between about 30% and about 80% byweight, between about 50% and about 70% by weight, and between about 60%and about 80% by weight. Furthermore, the silicon particles may or maynot be pure silicon. For example, the silicon particles may besubstantially silicon or may be a silicon alloy.

In one embodiment, the silicon alloy includes silicon as the primaryconstituent along with one or more other elements.

In an example scenario, the battery 100 may comprise a solid, liquid, orgel electrolyte. The separator 103 preferably does not dissolve intypical battery electrolytes such as compositions that may comprise:Ethylene Carbonate (EC), Fluoroethylene Carbonate (FEC), F2EC, VC,Propylene Carbonate (PC), Dimethyl Carbonate (DMC), Ethyl MethylCarbonate (EMC), Diethyl Carbonate (DEC), etc. with dissolved LiBF₄,LiAsF₆, LiPF₆, LiTFSI, LiFSI, LiDFOB, LiBOB, LiTDI, and LiClO₄ etc. Theseparator 103 may be wet or soaked with a liquid or gel electrolyte. Inaddition, in an example embodiment, the separator 103 does not meltbelow about 100 to 120° C., and exhibits sufficient mechanicalproperties for battery applications. A battery, in operation, canexperience expansion and contraction of the anode and/or the cathode. Inan example embodiment, the separator 103 can expand and contract by atleast about 5 to 10% without failing, and may also be flexible.

The separator 103 may be sufficiently porous so that ions can passthrough the separator once wet with, for example, a liquid or gelelectrolyte. Alternatively (or additionally), the separator 103 mayabsorb the electrolyte through a gelling or other process even withoutsignificant porosity. The porosity of the separator 103 is alsogenerally not too porous to allow the anode 101 and cathode 105 totransfer electrons through the separator 103.

The anode 101 and cathode 105 comprise electrodes for the battery 100,providing electrical connections to the device for transfer ofelectrical charge in charge and discharge states. The anode 101 maycomprise silicon, carbon, or combinations of these materials, forexample. Typical anode electrodes comprise a carbon material thatincludes a current collector such as a copper sheet. Carbon is oftenused because it has excellent electrochemical properties and is alsoelectrically conductive. Anode electrodes currently used in rechargeablelithium-ion cells typically have a specific capacity of approximately200 milliamp hours per gram (mAh/g). Graphite, the active material usedin most lithium ion battery anodes, has a theoretical energy density of372 mAh/g. In comparison, silicon has a high theoretical capacity of4200 mAh/g. In order to increase volumetric and gravimetric energydensity of lithium-ion batteries, silicon may be used as the activematerial for the cathode or anode. Silicon anodes may be formed fromsilicon composites, with more than 50% silicon, for example.

In an example scenario, the anode 101 and cathode 105 store the ion usedfor separation of charge, such as lithium. In this example, theelectrolyte carries positively charged lithium ions from the anode 101to the cathode 105 in discharge mode, as shown in FIG. 1 for example,and vice versa through the separator 105 in charge mode. The movement ofthe lithium ions creates free electrons in the anode 101 which creates acharge at the positive current collector 1078. The electrical currentthen flows from the current collector through the load 109 to thenegative current collector 107A. The separator 103 blocks the flow ofelectrons inside the battery 100, allows the flow of lithium ions, andprevents direct contact between the electrodes.

While the battery 100 is discharging and providing an electric current,the anode 101 releases lithium ions to the cathode 105 via the separator103, generating a flow of electrons from one side to the other via thecoupled load 109. When the battery is being charged, the oppositehappens where lithium ions are released by the cathode 105 and receivedby the anode 101.

Reliability and energy density of the battery 100 are dependent upon thematerials selected for the anode 101 and cathode 105. The energy, power,cost, and safety of current Li-ion batteries need to be improved inorder to, for example, compete with internal combustion engine (ICE)technology and allow for the widespread adoption of electric vehicles(EVs). High energy density, high power density, and improved safety oflithium-ion batteries may be achieved with the development ofhigh-capacity and high-voltage cathodes, high-capacity anodes, andfunctionally non-flammable electrolytes with high voltage stability andinterfacial compatibility with electrodes. In addition, materials withlow toxicity are beneficial as battery materials to reduce process costand promote consumer safety.

The performance of electrochemical electrodes are depending upon manyfactors including the robustness of electrical contact between electrodeparticles, as well as between the current collector and the electrodeparticles. The electrical conductivity of silicon anode electrodes maybe manipulated by incorporating conductive additives with differentmorphological properties. Carbon black (SuperP), vapor grown carbonfibers (VGCF), and a mixture of the two have may be incorporatedseparately into the anode electrode resulting in improved performance ofthe anode. The synergistic interactions between the two carbon materialsmay facilitate electrical contact throughout the large volume changes ofthe silicon anode during charge and discharge.

State-of-the-art lithium-ion batteries typically employ agraphite-dominant anode as an intercalation material for lithium. Withdemand for lithium-ion battery performance improvements such as higherenergy density and fast-charging, silicon may be added as an activematerial or even completely replacing graphite as a dominant anodematerial. Most electrodes that are considered “silicon anodes” in theindustry are graphite anodes with silicon added in small quantities(typically <20%). These graphite-silicon mixture anodes must utilize thegraphite, which has a lower lithiation voltage compared to silicon; thesilicon has to be nearly fully lithiated in order to utilize thegraphite. Therefore, these electrodes do not have the advantage of asilicon or silicon composite anode where the voltage of the electrode issubstantially above OV vs Li/Li+ and thus are less susceptible tolithium plating. Furthermore, these electrodes can have significantlyhigher excess capacity on the silicon versus the opposite electrode tofurther increase the robustness to high rates.

Silicon-based anodes have a lithiation/delithiation voltage plateau atabout 0.3-0.4V vs. Li/Li+, which allows it to maintain an open circuitpotential that avoids undesirable Li plating and dendrite formation.While silicon shows excellent electrochemical activity, achieving astable cycle life for silicon-based anodes is challenging due tosilicon's large volume changes during lithiation and delithiation.Silicon regions may lose electrical contact from the anode as largevolume changes coupled with its low electrical conductivity separate thesilicon from surrounding materials in the anode.

In addition, the large silicon volume changes exacerbate solidelectrolyte interphase (SEI) formation, which can further lead toelectrical isolation and, thus, capacity loss. Expansion and shrinkageof silicon particles upon charge-discharge cycling causes pulverizationof silicon particles, which increases their specific surface area. Asthe silicon surface area changes and increases during cycling, SEIformation repeatedly breaks apart and reforms. The SEI formation thuscontinually builds up around the pulverizing silicon regions duringcycling into a thick electronic and ionic insulating layer. Thisaccumulating SEI formation increases the impedance of the electrode andreduces the electrode electrochemical reactivity, which is detrimentalto cycle life.

Therefore, there is a trade-off among the functions of active materials,conductive additives, and polymer binders. The balance may be adverselyimpacted by high energy density silicon anodes with low conductivity andhuge volume variations described above. This disclosure address thisissue through the use of primary resin carbon precursors comprisingwater soluble acidified polyamide-imide (PAI) (e.g. 5-8%) and variouspolymeric stabilizing additives such as polyacrylic acid (PAA) solution,poly (maleic acid, methyl methacrylate/methacrylic acid,butadiene/maleic acid) solutions, water soluble carboxyl acid groupcontaining (co)polyimide solution, and other soluble polymers containingcarboxyl acid groups. These polymeric stabilizing additives may assistin the stabilizing the slurry, and may also serve as a carbon source. Insome embodiments, the primary resin carbon precursor comprises anaqueous solution of two or more polymers.

Further water soluble polymers that may be used as polymeric stabilizingadditives include, but are not limited to, one or more ofPolyamide-imide {Includes International-innotek (GT-720W, GT-721W,GT-722W), China-innotek (PIW-015, PIW-025, PIW-026), Elantas (Elan-bind1015, Elan-bind 1015 NF), Solvay Torlon AI series (AI30, AI30-LM, AI10,AI10-LM)}; Polyimide; Ammonium Lignosulfonate; Kraft Lignin; Dextran;Pullulan (polysaccharide polymer); Phenolic resins {Includes(Plenco(Novolac Resins), Resol Resins, polymethylol phenol, ERPENE PHENOLICRESIN (emulsion)}; Formaldehyde based Resins; Melamine-formaldehydebased resins; Silane based resins (gelest); Polyurethanes; TOCRYL(acrylic emulsion); Chitosan; Helios Resins {Includes (DOMOPOL,DOMACRYL, DOMALKYD and DOMEMUL}; Polymethyl methacrylate;Poly(methacrylic acid); Poly(vinyl acetate)/poly(vinyl alcohol)complexes; ACRONAL water-based acrylic and stryrene-acrylic emulsionpolymers; STYROFAN carboxylated styrene-butadiene binders; Solic AcrylicResin; Rotaxane; Poly(acrylic acid); Cellulose; Starch; Polysacharides;Glycogen; Carbohydrates (other); and polymers with the followingbackbones Sucrose, Glucose, Sucralose, Xylitol, Sorbitol, Sucralose,Glucosidases, Galactose, and Maltose.

Further additives may be used in order to modify the characteristics ofthe polymer solution. Suitable additives include, but are not limitedto, one or more of Poly(acrylic acid), Carboxymethylcellulose (CMC),Polyvinylpyrrolidone, Myo-Inositol, Mannitol, Pinitol, Ribose, Sorbitol,Fucose, Maltodextrin, Ganglioside, Maltose, Sucrose, Glucose, Sucralose,Xylitol, Fructose, Palatinose hydrate, Dextran sucrase, Guanosine,Inulin, Sucrose phosphorylase, Glucosidases, AmberLite, Raffinose,Mannose, Psicose, Hexokinase, NADHs, Phosphoglucose, Phosphomannose,Topiramate, Furfurals, Nuciferine, Galactose, and Maltose. In someembodiments these additives may be added to the resin to increase itsviscosity (e.g. by >10%) to facilitate the processing of the slurry andimprove the coating quality.

Water-soluble PAI (WPAI) material has a polyamide-imide (PAI) backbone,but the polymer is functionalized with acidic groups (such as carboxylicacid) to allow the polymer to dissolve in water, so WPAI is a PAI analogwith acidic functional groups added to the chemical formula. Watersoluble PAI is similar in chemical structure to PAI, however acid groupssuch as carboxylic acid or amic acid are embedded into the polymerbackbone.

Water-soluble acidified PAI and water-based acidic polymer solutionadditive anodes provide the benefits of improved cycle life, increasedenergy density, increased power density, improved flexibility, improvedadhesion, and reduced cost. Water-soluble acidified PAI and water-basedacidic polymer solution additive electrodes may also provide improvedsafety. WPAI polymers can contain water; for example, WPAI polymer canhave a water content of 45-75%, in some embodiments, the water contentis 65%. Additional water may still be needed to dissolve the polymerabove the water content already present in the polymer.

As discussed above, water soluble acidified PAI is a WPAI having a PAIbackbone, functionalized with acidic groups to allow the polymer todissolve in water. Acidic functional groups that may be used tofunctionalize PAI include, but are not limited to, one or more of Amicacid, Butane tetracarboxylic acid (BTC), Tetracarboxylic acid (TC),Carboxylic acid, Licanic acid, Methacrylic acid, Acetic acid,Aminomethanesulfonic acid, Anthranilic acid, Benzenesulfonic acid,Benzoic acid, Camphor-10-sulfonic acid, Citric acid, Folic acid, Formicacid, Fumaric acid, Gallic acids, Lactic acid, Maleic acid, Malonicacid, Methanesulfonic acid, Nitrilotriacetic acid, Oxalic acid,Peracetic acid, Phthalic acid, Propionic acid, Salicylic acid, Sorbicacid, Succinic acid, Sulfamic acid, Sulfanilic acid, Tannic acid,Thioacetic acid, Trifluoromethanesulfonic acid, Acrylic acids,Aminophenylboronic acid, and Fuconic acid. In further embodiments,non-acidic groups may be used to functionalize the PAI such asPhosphates (including phosphate esters and phosohate diesters),Ranirestat, and Phosphatase.

FIG. 2A is a flow diagram of a direct coating process for fabricating acell with a silicon-dominant electrode, in accordance with an exampleembodiment of the disclosure. This process comprises physically mixingthe electrode coating layer and conductive additive together, andcoating it directly on a current collector as opposed to forming theelectrode coating layer on a substrate and then laminating it on acurrent collector. This strategy may also be adopted by otheranode-based cells, such as graphite, conversion type anodes, such astransition metal oxides, transition metal phosphides, and other alloytype anodes, such as Sn, Sb, Al, P, etc.

In step 201, the raw electrode coating layer may be mixed to form aslurry with stable viscosities of more than 1500 cp by usingwater-soluble acidified PAls (WPAI) and water-based acidic polymersolution additives. The addition of the polymer solution additiveenables the adjustment of the viscosity of the polymer andhomogenization of the slurry. The fabricated anode shows superioradhesion to copper, a remarkable cohesion, and exceptional flexibility.This anode is shown to be capable of fast charging and performs similaror better than current anodes.

The particle size and mixing times may be varied to configure theelectrode coating layer density and/or roughness. Furthermore, cathodeelectrode coating layers may be mixed in step 201, where the electrodecoating layer may comprise lithium cobalt oxide (LCO), lithium ironphosphate, lithium nickel cobalt manganese oxide (NMC), Ni-rich lithiumnickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO),lithium nickel manganese spinel, LFP, Li-rich layer cathodes, LNMO orsimilar materials or combinations thereof, mixed with carbon precursorand additive as described above for the anode electrode coating layer.

As described herein, aqueous-based polyamide-imide resins used tofabricate silicon dominant anodes are disclosed. Environmentallyfriendly bases may be used in the slurry and stabilizers may also beused. In some embodiments, water soluble PAI (5-20% in water) is used asa carbon source (precursor), triethanolamine is used as base and PAA asstabilizer to create high silicon content anodes.

The slurry may be made in water and may have varying composition. In oneembodiment, the slurry may contain one or more of the followingcomponents in the following ranges:

-   -   DI water: 30-70%    -   Polymer solids: between 5-35%    -   Base: less than 30%    -   Acid: less than 25%    -   Surfactant: less than 5%    -   Other polymer additives: less than 40%.

Bases that can be used in the slurry include, but are not limited to,one or more of Triethanolamine, Triethylamine, N-Methyldiethanolamine,Butyldiethanolamine, Diethylamine, Ethylamine, Tetrabutylammoniumhydroxide, Tetramethylammonium hydroxide, Tetramethylammonium hydroxide,Triisopropanolamine, Trolamine, Amino-2-propanol, Triisobutylamine,N-Isopropyl-N-methyl-tert-butylamine, 2-Amino-2-methyl-1-propanol,1-Amino-2-butanol, 2-Amino-1-butanol, Diethanolamine, Ethanolamine,2-Dimethylaminoethanol, N-Phenyldiethanolamine, 2-(Dibutylamino)ethanol,2-(Butylamino)ethanol, N-tert-Butyldiethanolamine,N-Ethyldiethanolamine, Avridine, and 2-(Diisopropylamino)ethanol.

In some embodiments, aqueous-based polyamide-imide resins are used tocreate a slurry containing an environmentally friendly base (such astriethanolamine) along with polyacrylic acid (PAA). In this slurry, PAIis used as the main carbon source, triethanolamine as the base, and PAAboth as the slurry stabilizer and as carbon source. The environmentallyfriendly base (such as triethanolamine) is a non-corrosive amine basewhich facilitates the dissolution of the PAI in water.

In some embodiments, the slurry contains an optional surfactant.Addition of a surfactant may improve the coating quality. Suitablesurfactants include, but are not limited to, octyltrimethylammoniumbromide, dodecyltrimethylammonium bromide, cetyltrimethylammoniumbromide, Polyvinylpyrrolidone a-fluoro homoallylic alcohols,α-Cyclodextrin, TritonX-100, FluorN 561 and FluorN 562, ETI 929 (fromEnvTech), alkyl glycosides, and TEGO® Surten E.

In an example embodiment, for a silicon-dominant anode, 30-40 grams ofdry WPAI, 15-25 grams of a basic amine such as butyldiethanolamine ortriethanolamine, and 400-500 grams of water may be mixed at hightemperature to form a solution. Then, 30-50 grams of this solution maybe mixed with 5-20 grams of silicon microparticles (˜10-12 μm) plus0.2-0.5 grams of PAA 12% solution in water as additive, and 4-8 grams ofwater. The mixture may be mixed using a low shear mixer or a centrifugalspeed mixer, where FIG. 3 shows the changes in the viscosity of thesolution versus mixing time.

In a further example embodiment, for a silicon-dominant anode, a WPAIsolution was made using the following example formulation in Table 1.

TABLE 1 WPAI solution grams WPAI polymer 100 Water 458 triethanolamine27

To prepare the WPAI solution, 100 grams of the polymer powder (watercontent 45-75%) may be dissolved in a mixture of 458 grams of DI waterand 27 grams of triethanolamine. Then the temperature of the mixture maybe raised to >80° C. under vigorous stirring overnight to allow thepolymer to dissolve in the solution. Then the solution may be filteredto form the WPAI solution used to make the slurry.

In another example embodiment, WPAI-resin may be used to make a slurrywith various formulations having different types of silicon toillustrate that different silicon particles may be used. The formulationof the slurry was as follows in Table 2.

TABLE 2 Si 20.92% PAI-resin 66.90% Polyacrylic acid (12% in water) -12.07% PAA surfactant 0.10%

To prepare the slurries with different silicon particles, siliconpowders with different particle size (D50 of 5 μm and D50 of 12 μm) maybe added to a solution of the resin pre-mixed with the surfactant in theproportions set forth above in Table 2. Then PAA solution may be addedto the mixture and further mixed to form the slurry.

Three separate slurries may be prepared using the Table 2 formulationwith the following silicon powders:

-   -   Sample 1: Silicon powder with D50 of 12 μm    -   Sample 2: Silicon powder with D50 of 12 μm (80%) and D50 of 5 μm        (20%)    -   Sample 3: Silicon powder with D50 of 5 μm.        FIG. 8 shows the changes in the viscosity of the solution versus        temperature for Sample 3, above.

In step 203, the as-prepared slurry may be coated on a copper foil, 20μm thick in this example, and in step 205 may be dried at 130° C. in aconvection oven to dry the coating and form the green anode. Similarly,cathode electrode coating layers may be coated on a foil material, suchas aluminum, for example.

An optional calendering process may be utilized in step 207 where aseries of hard pressure rollers may be used to finish the film/substrateinto a smoother and denser sheet of material.

The slurries from Samples 1-3 above may be coated separately on 15 μmcopper foils and pyrolyzed under Argon gas at 650° C. for 3 hours toform silicon dominant anodes. Testing may be performed between 4.2V-2Vusing the sample anodes and NMC cathode. The electrochemical performanceof the anodes in pouch cells is shown in FIG. 9 .

In step 209, the electrode coating layer may be pyrolyzed by heating to500-800° C., 650° C. in this example, in an inert atmosphere such thatcarbon precursors are partially or completely converted into conductivecarbon. The pyrolysis step may result in an anode electrode coatinglayer having silicon content greater than or equal to 50% by weight,where the anode has been subjected to heating at or above 400 degreesCelsius. In one embodiment the pyrolysis conditions may be between450-800° C., under Argon, Nitrogen, or Forming gas.

Pyrolysis can be done either in roll form or after punching in step 211.If done in roll form, the punching is done after the pyrolysis process.In instances where the current collector foil is notpre-punched/pre-perforated, the formed electrode may be perforated witha punching roller, for example. The punched electrodes may then besandwiched with a separator and electrolyte to form a cell. In step 213,the cell may be subjected to a formation process, comprising initialcharge and discharge steps to lithiate the anode, with some residuallithium remaining, and the cell capacity may be assessed.

FIG. 2B is a flow diagram of an alternative process for lamination ofelectrodes, in accordance with an example embodiment of the disclosure.While the previous process to fabricate composite anodes employs adirect coating process, this process physically mixes the activematerial, conductive additive, and binder together coupled with peelingand lamination processes.

This process is shown in the flow diagram of FIG. 2B, starting with step221 where the raw electrode coating layer may be mixed to form a slurrywith stable viscosities of more than 1500 cp by using water-solubleacidified PAIs (WPAI) and water-based acidic polymer solution additives.The addition of the polymer solution additive enables the adjustment ofthe viscosity of the polymer and homogenization of the slurry.

The particle size and mixing times may be varied to configure theelectrode coating layer density and/or roughness. Furthermore, cathodeelectrode coating layers may be mixed in step 221, where the electrodecoating layer may comprise lithium cobalt oxide (LCO), lithium ironphosphate, lithium nickel cobalt manganese oxide (NMC), Ni-rich lithiumnickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO),lithium nickel manganese spinel, LFP, Li-rich layer cathodes, LNMO orsimilar materials or combinations thereof, mixed with carbon precursorand additive as described above for the anode electrode coating layer.

In an example embodiment, for a silicon-dominant anode, 30-40 grams ofdry WPAI, 15-25 grams of a basic amine such as butyldiethanolamine ortriethanolamine, and 400-500 grams of water may be mixed at hightemperature to form a solution. Then, 30-50 grams of this solution maybe mixed with 5-20 grams of silicon microparticles (˜10-12 μm) plus0.2-0.5 grams of PAA 12% solution in water as additive, and 4-8 grams ofwater. The mixture may be mixed using a low shear mixer or a centrifugalspeed mixer, where FIG. 3 shows the changes in the viscosity of thesolution versus mixing time.

In step 223, the slurry may be coated on a polymer substrate, such aspolyethylene terephthalate (PET), polypropylene (PP), or Mylar. Theslurry may be coated on the PET/PP/Mylar film at a loading of 3-6 mg/cm²for the anode and 15-35 mg/cm² for the cathode, and then dried in step225. An optional calendering process may be utilized where a series ofhard pressure rollers may be used to finish the film/substrate into asmoothed and denser sheet of material.

In step 227, the green film may then be removed from the PET, where theactive material may be peeled off the polymer substrate, the peelingprocess being optional for a polypropylene (PP) substrate, since PP canleave ˜2% char residue upon pyrolysis. The peeling may be followed by acure and pyrolysis step 229 where the film may be cut into sheets, andvacuum dried using a two-stage process (100-140° C. for 14-16 hours,200-240° C. for 4-6 hours). The dry film may be thermally treated at1000-1300° C. to convert the polymer matrix into carbon.

In step 231, the pyrolyzed material may be flat press or roll presslaminated on the current collector, where for aluminum foil for thecathode and copper foil for the anode may be pre-coated withpolyamide-imide with a nominal loading of 0.35-0.75 mg/cm² (applied as a5-7 wt % varnish in NMP, dried 10-20 hour at 100-140° C. under vacuum).In flat press lamination, the active material composite film may belaminated to the coated aluminum or copper using a heated hydraulicpress (30-70 seconds, 250-350° C., and 3000-5000 psi), thereby formingthe finished composite electrode. In another embodiment, the pyrolyzedmaterial may be roll-press laminated to the current collector.

In step 233, the electrodes may then be sandwiched with a separator andelectrolyte to form a cell. The cell may be subjected to a formationprocess, comprising initial charge and discharge steps to lithiate theanode, with some residual lithium remaining, and testing to assess cellperformance.

FIG. 3 illustrates slurry viscosity versus mixing time, in accordancewith an example embodiment of the disclosure. The plot indicates that aslurry with stable viscosity can be achieved using WPAI as the carbonprecursor, where a viscosity of 1500 centipoise (cp) may be obtainedafter ˜15 hours with this mixture. The polymer additive may play a rolein linking long chain PAls together and as a result increases theviscosity of the solution.

FIG. 4 illustrates the results of thermal gravimetric analysis (TGA) ofdry WPAI, in accordance with an example embodiment of the disclosure.The TGA analysis may be performed under nitrogen atmosphere with a flowrate of 100 sccm and temperature ramp rate of 5° C./min. The plot showsthe weight percentage remaining and the normalized heat flow provided tothe material in W/g over a temperature range up to 800° C. The TGAanalysis indicates that the polymer has ˜58% char yield at 650° C. andmore than 53% char yield at 800° C.

FIG. 5 illustrates an adhesion test for a silicon-dominant anode withwater-soluble acidified PAI and water-based acidic polymer solutionadditive, in accordance with an example embodiment of the disclosure.The test setup includes a clamp 501 for holding an electrode 505fastened to a glass slide 503 using adhesive tape (not visible) holdingthe anode on one side on the other is a double sided adhesive tape (notvisible) for coupling to weights.

The anode shows a superior adhesion strength, with capability of holding350 grams of weights before the coating detaches from the copper. Suchadhesion is much higher than most anodes which mostly fail to hold morethan 50 grams of weights.

FIG. 6 illustrates a silicon-dominant anode after a winding test, inaccordance with an example embodiment of the disclosure. In thisexample, the anode is wrapped around a 4 mm mandrel in order to test thefeasibility of using it for cylindrical cells. As it can be seen fromFIG. 6 , the anode shows only minor cracks, no copper exposures due tocarbon detachments, and no flaking. Therefore, such a remarkableflexibility and anode integrity indicates that the water-based slurryanode is appropriate for use in cylindrical cells.

FIG. 7 illustrates normalized discharge capacity of a cell withwater-soluble acidified PAI and water-based acidic polymer solutionadditive anode compared to a standard cell with NMP-based resinlaminated anode, in accordance with an example embodiment of thedisclosure. The plot compares the normalized capacity retention of thestandard anode (solid line—anode laminated on a current collector withan adhesive) versus the water-soluble acidified PAI and water-basedacidic polymer solution additive anode (dashed line). The NMP-basedresin anode may be laminated on a copper foil coated with PAI adhesive,as opposed to the direct-coated water-based resin anode.

While the absolute capacity values indicate that both anodes havesimilar capacities, the normalized capacity values shown indicate thatthe water-soluble acidified PAI anode demonstrates a better capacityretention compared with the standard anode. The standard anode in thisexample is a free standing pyrolyzed coupon that is laminated onadhesive-coated copper. As can be seen in FIG. 7 , the water-solubleacidified PAI anode is still at near 100% discharge capacity after 60cycles. In addition to improved cycle life, water-soluble acidified PAIand water-based acidic polymer solution additive anodes demonstrateincreased energy density, increased power density, improved flexibility,improved adhesion, and reduced cost using water soluble acidified PAI.

FIG. 8 illustrates slurry viscosity against temperature for a samplecontaining silicon powder with D50 of 5 μm at 20.92%, PAI-resin at66.90%, Polyacrylic acid (12% in water)-PAA at 12.07% and surfactant at0.10%, at 60 and 100 RPM.

FIG. 9 illustrates electrochemical performance of the anodes in pouchcells, where the anodes are made from slurries according to Samples 1-3above. The cycling may be performed at 2C charge and 0.5C dischargebetween 4.2-2.5V.

FURTHER EXAMPLES AND EMBODIMENTS

The following provides further examples and/or embodiments ofsilicon-dominant anodes and processes for manufacturing suchsilicon-dominant anodes. In the interest of brevity, thesilicon-dominate anodes are described below as being manufactured perthe direct coating process of FIG. 2A. However, each of the belowsilicon-dominant anodes may be manufactured per the direct coatingprocess of FIG. 2A or the laminating process of FIG. 2B.

A silicon-dominate anode was prepared based on the following slurryformulation, which is presented in mass units in Table 3 and as weightpercentages in Table 4:

TABLE 3 Silicon powder 10.461 g PAI solution in DI water (6%) 33.457 gPolyacrylic acid solution in water (12%) 6.037 g Surfactant 0.045 g

TABLE 4 Silicon powder 20.9% PAI solution in DI water (6%) 66.9%Polyacrylic acid solution in water (12%) 12.1% Surfactant 0.1%

In particular, the slurry was formed at 201 of FIG. 2A from the abovecomponents by adding the surfactant and PAI solution to a mixer. Themixer mixed the surfactant and PAI solution at 2000 rpm for 1 minute.The silicon powder was then added to the mixer and mixed at 2000 rpm foranother minute. Then, the PAA solution was added to the mixer and mixedat 2000 rpm for another minute. At which point, the mixture was filteredthrough a 120 μm mesh to remove agglomerates and returned to the mixer.The mixer further mixed the slurry at 2000 rpm for a minute and then at2200 rpm for another minute.

At 203, the slurry was coated on a foil. In particular, the slurry washand coated using a 9 mil doctor blade on one side of a 20 μm copperfoil. In particular, the copper foil was a rolled copper foil made ofC15500 alloy and the slurry was applied to a thickness of about 30 μm,resulting in a copper foil to active material thickness ratio of about0.66 (20 μm/30 μm). Some embodiments may utilize a copper foil made ofC15500, C19400, C26000, or C51000 copper alloys.

At 205, the slurry coated copper foil was dried at about 90° C. in agravity convection oven for 10 to 15 minutes, then slit into 2-inch wideanode stripes. The anode stripes were further dried at 80° C. undervacuum overnight before calendering. At 207, the anode stripes werecalendered using a fixed gap calendering machine at 60° C. to reachdesigned thickness of 50-65 μm including 20 μm Cu foil and density ofapproximately 1.0-1.1. After calendering, the anode stripes were punchedto form anode coupons and the anode coupons at 209 were pyrolyzed at650° C. with 5° C./min ramp and 180 minute dwell time in an Argonatmosphere. Such process resulted in single-side anodes having an activematerial layer of about 30 μm on one side of the copper foil. The finalcomposition of the anode active material after pyrolysis was about 86%silicon and about 14% pyrolytic carbon. Moreover the active material hada porosity of about 50-56%.

Some embodiments of a silicon-dominant anode may utilize a foilthickness to active material layer thickness of over 0.5, wherein theporosity of the active material layer is below 70%. Some embodiments ofa silicon-dominant anode may utilize a foil thickness to active materiallayer thickness of 0.15, about 0.15, over 0.15, 0.25, about 0.25, over0.25, 0.5, about 0.5, over 0.5, 0.66, about 0.66, or over 0.66, whereinthe porosity of the active material layer is 70%, about 70%, below about70%, 60%, about 60%, below about 60%, 50%, about 50%, below about 50%,40%, about 40%, below about 40%, 30%, about 30%, or below about 30%.

Moreover, some embodiments of a silicon dominant anode may utilize afoil thickness to porosity-adjusted active material layer thicknessratio of 0.25, about 0.25, over 0.25, 0.33, about 0.33, over 0.33, 0.5.,about 0.5, over 0.5, 0.6, about 0.6, over 0.6, 1, about 1, over 1, 1.3,about 1.3, or over 1.3. Such ratio may be calculated per Equation 1:

$\begin{matrix}\frac{{foil}{thickness}}{{active}{material}{thickness} \times ( {1 - \frac{{porosity}{in}{percentage}}{100}} )} & {{Equation}1}\end{matrix}$

Single-layer pouch cells were then constructed from the single-sidedanodes. In particular, each pouch cell included one single-layer anode,one double layer cathode, and about 1 mL of electrolyte, providing anapproximate capacity of 78 mAh. The cathode facing pouch side was tapedusing Kapton tape to avoid/minimize electrochemical reactions. Eachsingle-layer pouch cell was subject to a hot pressing step, a coldpressing step, or skipped the pressing step, before going throughformation and degassing. Afterwards, each single-layer pouch cell wasclamped between a bottom metal plate and top metal plate and tested in abattery tester. In particular, each single-layer cell was clamped in theorder of a bottom metal plate, paper, cell, foam pad, top metal plateusing fixed gap.

Some embodiments of the single-layer pouch cells may be assembled usinga fixture where the pressure is maintained by clamping the cell at acertain gap or using springs, actuators or other means to achieve apressure within about 10%, about 11%, about 15%, or about 20% oforiginal pressure (about 120 kPa). In some embodiments, the pressure maybe applied using compressible foam, metal springs, air bladder, paper,or fabric.

Some embodiments of the single-layer pouch cells may have an electrolyteto Ah ratio of about 2 g/Ah, over 2 g/Ah, about 2.4 g/Ah, over 2.4 g/Ah,about 5 g/Ah, over 5 g/Ah, about 10 g/Ah, over 10g/Ah, about 16 g/Ah,over 16 g/Ah.

Some embodiments of the single-layer pouch cells may be sealed withexcess pouch material on at least one side. For example, the seal may beat least 5 mm, at least 3 mm, or at least 2 mm from an edge of the cellstack.

In some embodiments of the single-layer pouch cells, thesilicon-dominate anode may have an areal capacity between 9 mAh/cm² and15 mAh/cm². Moreover, the amount of electrolyte per active area of theelectrode may be between 0.02 and 0.1 mL/cm². The active area of theelectrode corresponds to the area of the silicon-dominate anode in cm²that participates in the electrochemical reaction. In some embodiments,the silicon-dominate anode may have an areal capacity between 5 mAh/cm²and 11 mAh/cm² with the amount of electrolyte per active area ofelectrode between 0.005 and 0.05 m L/cm².

The performance of the single-layer pouch cells were then compared tofive-layer pouch cells. Each of the five-layer pouch cells included sixlayers of double-sided anodes and five layers of double-sided cathodes.The anodes of the five-layer pouch cells were made using the sameformulation and mixing method as the single-layer pouch cells. Theanodes of the five-layer pouch cells used a 15 μm foil with an activematerial thickness of about 30 μm on each side, thus resulting in acopper foil to active material thickness ratio of about 0.66 (20 μm/3020 μm). Each single-layer pouch cell provided 78 mAh measured between4.2 V and 2.75 V at 0.5C. Conversely, each five-layer pouch cellprovided 780 mAh measured between 4.2 V and 2.75 V at 0.5C.

Referring now to FIG. 10 , capacity retention of single-layer pouchcells (enhanced cells) and five-layer pouch cells (baseline cells) aredepicted for cycle life based on 2C (4.2 V)/0.5C (2.75 V) cycles. Inparticular, the enhanced cells and baseline cells of FIG. 10 includeanodes manufactured per the formulation of Table 3 and process describedabove. As shown by lines 1000, the baseline cells reached their 80%retention mark at about 160 cycles. However, as shown by lines 1010, theenhanced cells reached their 80% retention mark at about 220 cycles.

Referring now to FIG. 11 , capacity retention of single-layer pouchcells (enhanced cells) and five-layer pouch cells (baseline cells) aredepicted for cycle life based on 4C (4.2 V)/0.5C (3.2 V) cycles. Inparticular, the enhanced cells and baseline cells of FIG. 11 includeanodes manufactured per the formulation of Table 3 and process describedabove. Lines 1100 depict capacity retention of the baseline cells,whereas lines 1110 depict capacity retention of the enhanced cells. Asshown, the enhanced cells retained a greater amount of the originalcapacity after about 120 cycles than the baseline cells.

Referring now to FIG. 12 , a comparison is presented for capacityretention of pressed and not pressed pouch cells during cycle life basedon 2C (4.2 V)/0.5C (2.75 V) cycles. In particular, pressed and notpressed pouch cells include anodes manufactured per the formulation ofTable 3 and process described above. The pressed cells (shown by lines1200) include single-layer pouch cells subjected to a hot pressingprocess in which the cells were pressed at 140 psi at 100° C. for 2minutes and single-layer pouch cells subject to a cold pressing processin which the cells were pressed at 140 psi at room temperature. The notpressed cells (shown by lines 1210) were not subjected to either hotpressing or cold pressing processes. While a bit difficult to see, thelines 1210 of the not pressed cells closely track the lines 1200 for thepressed cells for the first 30 cycles. FIG. 12 does not include data forthe not pressed cells beyond the first 30 cycles. Per FIG. 12 , pressingdoes provide a significant factor of capacity retention for at least thefirst 30 cycles of cycle life based on 2C(4.2V)/0.5C(2.75V) cycles.

Referring now to FIG. 13 , a comparison is presented for capacityretention of single-layer pouch cells having anodes manufactured perthree different formulations, which are referred to as enhanced cell,enhanced cell 2, and enhanced cell 3 in FIG. 13 . The enhanced cells arerepresented by lines 1310 in FIG. 13 . Each enhanced cell includes ananode manufacture per the formulation of Table 3 and the above describedprocess.

The enhanced cells 2 are represented by lines 1320 in FIG. 13 . Eachenhanced cell 2 includes an anode manufactured per the formulation ofTable 5 and the above described process.

TABLE 5 Silicon powder 29.90% PAI solution (9.5%) in DI water 69.95%Surfactant 0.15%

After pyrolysis, the composition for the anode active material ofenhanced cell 2 was about 90% silicon and about 10% pyrolytic carbon.Moreover, the active material of each enhanced cell 2 had a porosity ofabout 50-56%.

The enhanced cells 3 are represented by lines 1330 in FIG. 13 . Eachenhanced cell 3 includes an anode manufactured per the formulation ofTable 6 and the above described process.

TABLE 6 Silicon powder 34.50% PAI solution (9.5%) in DI water 64.56Carbon additives 0.77% Surfactant 0.17%

After pyrolysis, the composition for the anode active material ofenhance cell 3 was about 90% silicon, about 8% pyrolytic carbon, andabout 2% carbon additive. Moreover, the active material of each enhancedcell 3 had a porosity of about 50-56%.

In view of the above results, the single-layer pouch cells (e.g.,enhanced cell, enhanced cell 2, and enhanced cell 3) improve normalizedcapacity retention by about 50% for 2C (4.2V)/0.5C (2.75V) cycling whencompared to the five-layer pouch cells (e.g., baseline cells). Moreover,the single-layer pouch cells (e.g., enhanced cell, enhanced cell 2, andenhanced cell 3) reduce degradation by more than a factor of 3 (i.e.,has less than ⅓ the degradation) up to about 120 cycles for 4C(4.2V)/0.5C (3.2V) cycling when compared to the five-layer pouch cells(e.g., baseline cells).

In an example embodiment of the disclosure, a method and system isdescribed for water soluble weak acidic resins as carbon precursors forsilicon-dominant anodes. The battery electrode may comprise an electrodecoating layer on a current collector, where the electrode coating layeris formed from silicon and pyrolyzed water-soluble acidic polyamideimide resin carbon precursor. The electrode coating layer may comprise apyrolyzed water-based acidic polymer solution additive. The polymersolution additive may comprise one or more of: polyacrylic acid (PAA)solution, poly (maleic acid, methyl methacrylate/methacrylic acid,butadiene/maleic acid) solutions, and water soluble PAA. The electrodecoating layer may comprise conductive additives. The current collectormay comprise a metal foil, where the metal current collector comprisesone or more of a copper, tungsten, stainless steel, and nickel foil inelectrical contact with the electrode coating layer. The electrodecoating layer may comprise more than 70% silicon. The electrode may bein electrical and physical contact with an electrolyte, where theelectrolyte comprises a liquid, solid, or gel. The battery electrode maybe in a lithium ion battery.

As utilized herein, “and/or” means any one or more of the items in thelist joined by “and/or”. As an example, “x and/or y” means any elementof the three-element set {(x), (y), (x, y)}. In other words, “x and/ory” means “one or both of x and y”. As another example, “x, y, and/or z”means any element of the seven-element set {(x), (y), (z), (x, y), (x,z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means “one ormore of x, y and z”. As utilized herein, the term “exemplary” meansserving as a non-limiting example, instance, or illustration. Asutilized herein, the terms “e.g.,” and “for example” set off lists ofone or more non-limiting examples, instances, or illustrations. Asutilized herein, a battery, circuitry or a device is “operable” toperform a function whenever the battery, circuitry or device comprisesthe necessary hardware and code (if any is necessary) or other elementsto perform the function, regardless of whether performance of thefunction is disabled or not enabled (e.g., by a user-configurablesetting, factory trim, configuration, etc.).

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A battery cell comprising: a cathode; aseparator; an electrolyte; and an anode; wherein the anode comprises acurrent collector and active material layer on the current collector;wherein the active material layer comprises at least 50% silicon; andwherein the electrolyte comprises 0.02 to 0.1 mL/cm² of the anode thatparticipates in an electrochemical reaction.
 2. The battery cell ofclaim 1, wherein the electrolyte comprises 0.005 to 0.05 mL/cm² of theanode that participates in an electrochemical reaction.
 3. The batterycell of claim 1, wherein a ratio of the electrolyte to Ah for thebattery cell is between 2 g/Ah and 10 g/Ah.
 4. The battery cell of claim1, wherein a ratio of the electrolyte to Ah is between 2 g/Ah and 5g/Ah.
 5. The battery cell of claim 1, wherein a ratio of the electrolyteto Ah is between 2.4 g/Ah and 10 g/Ah.
 6. The battery cell of claim 1,wherein a ratio of the electrolyte to Ah is between 2.4 g/Ah and 5 g/Ah.7. The battery cell of claim 1, wherein a porosity of the activematerial layer is less than 70%.
 8. The battery cell of claim 1, whereina porosity of the active material layer is less than 60%.
 9. The batterycell of claim 1, wherein a porosity of the active material layer is lessthan 50%.
 10. The battery cell of claim 1, wherein a porosity of theactive material layer is less than 40%.
 11. The battery cell of claim 1,wherein a porosity of the active material layer is less than 30%. 12.The battery cell of claim 1, wherein a second ratio of a thickness ofthe current collector to a thickness of the active material layer isgreater than 0.5.
 13. The battery cell of claim 1, wherein a secondratio of a thickness of the current collector to a thickness of theactive material layer is greater than 0.66.
 14. The battery cell ofclaim 1, wherein a second ratio of a thickness of the current collectorto a porosity-adjusted active material layer thickness of the activematerial layer is greater than 0.25.
 15. The battery cell of claim 1,wherein a second ratio of a thickness of the current collector to aporosity-adjusted active material layer thickness of the active materiallayer is greater than 0.33.
 16. The battery cell of claim 1, wherein asecond ratio of a thickness of the current collector to aporosity-adjusted active material layer thickness of the active materiallayer is greater than 0.5.
 17. The battery cell of claim 1, wherein asecond ratio of a thickness of the current collector to aporosity-adjusted active material layer thickness of the active materiallayer is greater than 0.6.
 18. The battery cell of claim 1, wherein asecond ratio of a thickness of the current collector to aporosity-adjusted active material layer thickness of the active materiallayer is greater than
 1. 19. The battery cell of claim 1, wherein asecond ratio of a thickness of the current collector to aporosity-adjusted active material layer thickness of the active materiallayer is greater than 1.3.
 20. The battery cell of claim 1, wherein theactive material layer further comprises a pyrolyzed binder.